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Physics Astrophysics Astrophysics of Galaxies

astro-ph.GA Watch Astrophysics of Galaxies

Friday 18 September

Astrophysics of Galaxies

KiDS J1447-0149: The first spatially resolved spectroscopy of a relic galaxy beyond the local universe. An old high-dispersion core embedded in a compact rotating stellar structure

Johanna Hartke, Chiara Spiniello, Michele Cappellari et al. (+13 more)

Relic galaxies are the descendants of high-redshift compact quiescent systems. We present the first spatially resolved spectroscopic study of J1447-0149, a massive relic at $z=0.21$, observed with MUSE+AO. We characterize its kinematics and stellar population properties to probe its spatially resolved mass assembly history. We measured stellar kinematics with sub-kpc bin sizes, covering $\sim 1.4$ effective radii. We then used a coarser three-bin configuration informed by the kinematics to recover the higher-order velocity moments, $[\alpha/{\rm Fe}]$, stellar age and metallicity. We reconstructed the star formation history and computed the degree of relicness (DoR). MUSE data reveal a velocity gradient, showing that J1447-0149 is not purely pressure supported. The velocity-dispersion field displays a central peak, reaching $\sigma_\star=233\pm13\,{\rm km\,s^{-1}}$, substantially larger than previous seeing-limited measurements ($\sigma_{\star} =187 \pm 9\,{\rm km\,s^{-1}}$). The $h_3$–$V_\star$ anti-correlation and mildly positive $h_4$ values support a composite structure, with a rotating stellar component surrounding a compact dynamically hot core. This central, dispersion-dominated region is also the oldest and most metal-rich component. Its SFH rises rapidly, with the stellar mass assembled within $\sim2\,{\rm Gyr}$ after the Big Bang, and reaches ${\rm DoR}=0.9^{+0.1}_{-0.2}$. The two outer bins have a DoR value of ${\rm DoR}=0.8\pm0.2$, consistent with the central bin, but possibly indicating slightly longer formation times. Spatially resolved spectroscopy has been crucial to confirm the relic nature of J1447-0149, linking resolved morphology, kinematics, and stellar populations to constrain the early assembly of its central spheroid and surrounding disk.
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All authors Johanna Hartke, Chiara Spiniello, Michele Cappellari, Davide Bevacqua, Enrico Congiu, Anna Ferré-Mateu, Adriano Poci, Claudia Pulsoni, Magda Arnaboldi, Giuseppe D'Ago, Michalina Maksymowicz-Maciata, Paolo Saracco, Diana Scognamiglio, David A. Simon, Crescenzo Tortora, Petri Väisänen

Astrophysics of Galaxies

ALMA Chemical Evolution (ACE) survey: an overview – extending dust and gas inference to low metallicities at cosmic noon

Irene Shivaei, Gergő Popping, Leindert A. Boogaard et al. (+13 more)

The baryon cycle governs the exchange of gas, metals, and dust between galaxies and their environments, but simultaneous constraints on these constituents remain scarce beyond z~1. The ALMA Chemical Evolution (ACE) survey is a Cycle 11 ALMA Large Program designed to address this by studying the molecular gas, dust, and metal content of sub-solar metallicity at cosmic noon. ACE consists of CO(3-2) and dust continuum observations of 25 galaxies at z=2.0-2.5 with robust gas-phase metallicity measurements spanning ~35% to 83% of solar metallicity. The survey approximately doubles the number of unlensed main-sequence galaxies at z>1 with CO, dust-continuum and metallicity measurements and extends such studies to almost an order of magnitude lower stellar masses and metallicities than previous surveys. The ACE observations yield 17 CO detections and 17 Band 7 continuum (rest-frame ~270um) detections. CO detectability correlates most strongly with metallicity and stellar mass, while dust continuum detectability is more closely linked to star formation rate (SFR) and infrared luminosity. Using the ACE measurements, we derive a new empirical scaling relation linking CO(3-2) luminosity to stellar mass, SFR, and metallicity, providing a practical benchmark for estimating molecular gas content in low-mass, low-metallicity galaxies. The survey reveals several particularly intriguing systems, including some of the lowest-metallicity CO and dust detections currently known at z>1, galaxies with extreme gas and dust fractions, and systems exhibiting offsets between stellar, dust, and molecular gas emission. ACE provides the first comprehensive view of the interplay between molecular gas, dust, metals, and star formation in sub-solar metallicity galaxies at cosmic noon, enabling direct tests of models for baryon cycling, chemical enrichment, and dust evolution during the peak epoch of galaxy assembly.
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All authors Irene Shivaei, Gergő Popping, Leindert A. Boogaard, Alexandra Pope, Ivanna Langan, Roxana Popescu, Nikki N. Geesink, Manuel Solimano, Caitlin M. Casey, Maximilien Franco, Melanie Kaasinen, Bahram Mobasher, Desika Narayanan, Pablo G. Pérez-González, Naveen Reddy, Ryan Sanders

Astrophysics of Galaxies

Hierarchical Hub Formation in Mon~R2: Evidence for Cloud-to-core Gas Flows

L. K. Dewangan, O. R. Jadhav, A. K. Maity et al. (+2 more)

We present a multi-scale kinematic study of the hub-filament system in Mon R2 using JCMT $^{13}$CO(3–2) and ALMA C$^{18}$O(1–0) observations to investigate how molecular gas converges toward the central hub and connects across cloud-to-core scales. The $^{13}$CO data reveal several velocity-coherent filaments with diverse position angles converging toward the central region hosting massive stars and stellar clusters, where distinct velocity components become spatially superposed. Two dominant velocity regimes at $\sim$8.8–10.2 and $\sim$10.4–11.8 km s$^{-1}$ are identified, with their velocity separation decreasing toward the central hub. The position–position–velocity and longitude–velocity maps of the $^{13}$CO emission exhibit a butterfly/X-shaped morphology, consistent with converging motions. A phenomenological rotating-and-infalling envelope model reproduces the longitude-velocity morphology, indicating that rotation and infall may contribute to the observed kinematics, although the model does not uniquely identify the underlying mechanism. At higher resolution, the ALMA C$^{18}$O observations resolve the molecular gas into multiple velocity-coherent filaments spanning $\sim$8–13 km s$^{-1}$, with distinct kinematic domains at $\sim$9–10.5, 10.5–11.5, and 12–13 km s$^{-1}$ converging toward the hub. The ALMA and JCMT position-velocity diagrams show consistent velocity structures across their respective spatial scales, with the ALMA-resolved features embedded within the broader molecular-gas velocity field traced by JCMT, demonstrating a multi-scale kinematic connection. These results support a hierarchical picture in which converging flows and filamentary accretion contribute to hub growth and ongoing star formation in Mon R2, while other dynamical processes may also contribute to the observed kinematics.
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All authors L. K. Dewangan, O. R. Jadhav, A. K. Maity, Saurabh Sharma, Ram K. Yadav

Astrophysics of Galaxies

An Orbital Interpretation of Decreasing Galaxy Velocity Distance Relations in Systems Dominated by Giant Elliptical Galaxies

Rabia Melati, Takia Larbaoui, Mohammed Ridha Benzidane et al. (+1 more)

The persistence of approximately flat rotation curves observed in many galaxies, is commonly interpreted as evidence for extended dark matter halos or as an indication of modified gravitational laws at low accelerations. In this work, we investigate an alternative orbital framework for the large scale kinematics of galaxy systems dominated by giant elliptical galaxies. We propose that selected non active companion galaxies form gravitationally bound orbital systems around a dominant central elliptical galaxy, conceptually analogous to the Solar System Using galaxy group catalogs together with data from the NASA IPAC Extragalactic Database, we analyze three independent systems centered on M87, M60, and NGC 1399. Candidate companions are selected according to common observational and dynamical criteria, including their location within the adopted search volume, approximate spatial coplanarity, and consistency of the effective gravitational parameter (Geff). For the three systems, the resulting velocity distance relations exhibit clear decreasing trends with increasing distance from the central elliptical galaxy, qualitatively consistent with Keplerian like orbital dynamics.
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All authors Rabia Melati, Takia Larbaoui, Mohammed Ridha Benzidane, Mourad Lounis

Astrophysics of Galaxies · Cross-listed from hep-ph

The high-velocity dark matter halo of the Milky Way in light of the LZ 248 keV event

Ciaran A. J. O'Hare

The interpretation of high-energy nuclear recoil events in direct-detection experiments can depend sensitively on the poorly understood high-speed tail of the Galactic dark matter velocity distribution. This fact has been brought into sharper focus recently by an anomalous nuclear-recoil event at $E_R\approx248~\mathrm{keV}$ observed by the LZ experiment. If interpreted as caused by a dark-matter-induced recoil, kinematic constraints on many models imply this particle would have to emerge from the high-speed tail. Here, we re-assess this astrophysical uncertainty using Milky Way analogues from the IllustrisTNG and FIRE simulations. We find that the maximum laboratory-frame DM speed on June 16, when the event was observed, is $792.7^{+82.9}_{-95.6}\, \mathrm{km/s}$ (median and 95% containment across simulations), with a median very close to the fiducial SHM value. Modelling the tail of the velocity distribution in three dimensions is complicated by the fact that these simulated dark matter halos are anisotropic and are generically seen to spin in the same direction as the baryonic disk. However, we find that this does not reduce the maximum laboratory-frame DM speed because the approximately Gaussian azimuthal velocity distribution is negatively skewed by this co-rotation, rather than shifted by it. We illustrate these results in the context of an inelastic dark matter interpretation of the LZ event.
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Astrophysics of Galaxies

Fountain pattern of baryon cycle revealed in galaxy ecosystems

Chengyu Ma, Yangyao Chen, Enci Wang et al. (+11 more)

Baryons in galaxy ecosystems are believed to undergo continuous cycles of inflow and outflow, forming fountain-like patterns that encode key information about how galaxies acquire matter from their environments and respond through feedback. The presence of such baryon cycles has been inferred from pieces of observational evidence, but a concrete understanding remains elusive because individual galaxy ecosystems are diverse and dynamic. Here we introduce a stacking method that combines baryonic fields across ensembles of individual galaxy ecosystems to suppress irregularities and reveal the underlying pattern. Applied to a cosmological hydrodynamic simulation, this approach unveils strikingly regular patterns in gas properties across the full spatial extent of galaxy ecosystems, in close agreement with those inferred from observations. This method is straightforward to implement, allowing the processes shaping the gas-cycling pattern to be fully understood within the structure-formation paradigm, and a solid framework to be constructed for linking simulated galaxy ecosystems with observations.
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All authors Chengyu Ma, Yangyao Chen, Enci Wang, Houjun Mo, Huiyuan Wang, Tao Wang, Qirong Yuan, Min Du, Zhaozhou Li, Kai Wang, Cheqiu Lyu, Haoran Yu, Zeyu Chen, Xiaoxuan Chen

Astrophysics of Galaxies

From Observation to Ground Truth: Reconstruction Losses of Galaxy Imaging Under Heteroscedastic Noise

Renhao Ye, Shiyin Shen and Quanfeng Xu

Deep learning is widely used to analyze galaxy images, and the reconstruction loss determines which image features a model prioritizes during training. Mean squared error (MSE) and mean absolute error (MAE) correspond to homoscedastic Gaussian and Laplace likelihoods, respectively, whereas the inverse-variance-weighted $\chi^2$ loss accounts for the spatially varying uncertainties of heteroscedastic astronomical noise. Comparing how closely these objectives recover the underlying signal requires a ground truth (GT), which real observations cannot provide. We therefore generate noise-free galaxy images with IllustrisTNG, SKIRT, and GalaxyGenius, convolve them with a point-spread function (PSF) to define the GT, and construct noisy simulated observations. We train otherwise identical variational autoencoders (VAEs) with the three reconstruction losses and evaluate their outputs against the GT. Over most of the evaluated signal-to-noise ratio (SNR) range, the $\chi^2$-trained model yields lower relative reconstruction errors than the MSE- and MAE-trained models, indicating that inverse-variance weighting improves galaxy-image reconstruction under the heteroscedastic noise considered here.
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Astrophysics of Galaxies · Cross-listed from astro-ph.HE

A Gamma-ray Emitting Head-Tail Radio Galaxy Swimming Through the Hot Medium of the Merging Cluster Abell 3627

Vaidehi S. Paliya, M. Böttcher, Swayamtrupta Panda et al. (+4 more)

Head-tail radio sources are jetted active galactic nuclei (AGN) moving through the dense intracluster medium of galaxy clusters. They are extremely rare in the gamma-ray sky, likely because they are usually observed at large viewing angles. Therefore, every new gamma-ray detection of head-tail radio galaxies allows us to probe the origin of the high-energy emission in this unique class of AGN. Here we report, for the first time, the association of ESO~0137-G007 (z=0.016), a head-tail radio galaxy located at the outskirts of the merging cluster Abell 3627, with the gamma-ray source FL16Y~J1615.5$-$6034. The motion of the galaxy through the dense cluster environment and subsequent ram pressure and/or intracluster medium turbulence have led to the formation of a $>$500 kpc-long jet exhibiting a twisted, wiggly radio morphology. Its optical spectrum, obtained with the 4.1 m SOAR telescope, is devoid of emission lines, indicating that the underlying accretion activity is radiatively inefficient. From the measured line-of-sight stellar velocity dispersion, we estimate the mass of the central supermassive black hole to be $(3.36\pm1.32)\times10^9$ \Msun. We briefly discuss several radiative models to explain the observed broadband spectral energy distribution of ESO~0137$-$G007. We conclude that deeper multi-wavelength observations of this unique gamma-ray emitting head-tail radio galaxy will enable us to better understand the interaction of the jet with the hot cluster environment, thus setting the stage for the research of this class of AGN with the upcoming Square Kilometer Array.
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All authors Vaidehi S. Paliya, M. Böttcher, Swayamtrupta Panda, Kiran Wani, D. J. Saikia, Mahadev Pandge, C. S. Stalin

Astrophysics of Galaxies

A large overdensity of LRD-like galaxies discovered by JWST in the SPT2349-56 protocluster at z=4.30

Scott C. Chapman, Kedar A. Phadke, Nikolaus Sulzenauer et al. (+20 more)

We present 11 newly identified ultra-red galaxies selected with JWST/NIRCam in the core of the z=4.3 protocluster SPT2349-56. Although these sources are not yet spectroscopically confirmed, their extremely red colours (m200-m444 > 2.0 mag), strong spatial concentration, and number density - at least 2000 times that of comparable field populations - make a chance projected association unlikely. Their colours overlap those used to select the widely studied “little red dot” (LRD) population, although most of the sources are spatially resolved and are therefore better described as extended red dots (ERDs). The resolved morphologies disfavour continuum emission dominated by an unresolved active nucleus and imply a substantial stellar contribution. Deep ALMA observations put strong limits on obscured star formation, and the ERD population mostly lies significantly below the star-forming main sequence. One object, ERD1/Q1, is substantially brighter and more massive, lying far below the main sequence, making it a strong candidate for a massive quiescent galaxy. These JWST-selected red galaxies reveal a previously inaccessible population extending to lower luminosities and stellar masses than the Dusty Star Forming Galaxy (DSFG) population which characterizes the dense protocluster core. SPT2349-56 may therefore capture an early phase of cluster assembly in which extreme starbursts coexist with galaxies already transitioning toward the passive galaxies characteristic of mature cluster cores.
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All authors Scott C. Chapman, Kedar A. Phadke, Nikolaus Sulzenauer, Dazhi Zhou, Hollis Akins, Manuel Aravena, James R. Burgoyne, Caitlin M. Casey, Erin Foley, Leah Fryer, Ryley Hill, Nicholas LeVar, Monica Natalia Isla Llave, Matt Malkan, Vismaya Pillai, William Rasakanya, Manuel Solimano, Justin S. Spilker, Aurelie Torti, Joaquin D. Vieira, Fabio Vito, David Vizgan, George Wang

Astrophysics of Galaxies

Patchy Reionization Delays Quenching in Isolated Ultra-faint Dwarf Galaxies

Juyoung Kim, Myoungwon Jeon, Yumi Choi et al. (+1 more)

The spatially inhomogeneous nature of cosmic reionization is directly encoded in the quenching timescales of ultra-faint dwarf galaxies (UFDs). While most cosmological simulations employ a spatially uniform UV background (UVB) for computational efficiency, such homogeneous treatment may oversimplify the physical impact of reionization on UFDs, whose star formation histories (SFHs) are highly sensitive to local environments. Under these idealized, instantaneous UVB frameworks, star formation in UFDs is typically truncated abruptly at the onset of reionization, creating a tension with the extended and diverse SFHs observed in Local Group UFDs. To address this discrepancy, we perform high-resolution cosmological zoom-in simulations to contrast two distinct reionization models: a conventional uniform UVB and an on-the-fly radiative transfer (RT)-based patchy reionization model. We find that RT-based reionization delays star-formation quenching by ~440 Myr on average, a result consistent with recent observational constraints. However, this extended star formation does not necessarily leave a discernible imprint on the stellar metallicity distribution, indicating that the delay–while physically significant for gas dynamics–is still insufficient to drive substantial chemical enrichment. Our results emphasize the necessity of more realistic, patchy reionization modeling to explain the observed diversity of the Local Group population.
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All authors Juyoung Kim, Myoungwon Jeon, Yumi Choi, Sangmo Tony Sohn

Thursday 17 September

Astrophysics of Galaxies · Cross-listed from gr-qc

Granular Structure and Local de Broglie Wavelength in Fuzzy Dark Matter Halos

Flavio Rosales-Infante, Alejandro Quiñonez-Guerrero, Iván Álvarez-Rios et al. (+1 more)

We study the granular structure that emerges in a Fuzzy Dark Matter (FDM) halo formed through kinetic relaxation. After the system reaches a virialized core-halo structure, we separate the density field into a smooth spherical component and a residual density that contains the interference pattern characteristic of FDM halos. The power spectrum of this residual field shows a well defined dominant scale, different from the characteristic scale of the total density and of the smooth core-halo model. We compare this granular scale with a local de Broglie wave-lenght calculated from the velocity field obtained from the density current of the system. We find that both scales remain of the same order of magnitude, with the granular scale systematically smaller than the de Broglie wavelength. The radial behavior of the de Broglie wavelength also reveals a non-uniform internal structure, it decreases from the core and reaches its minimum near the transition between the solitonic core and the outer halo. These results provide a quantitative connection between density fluctuations, the local velocity field, and the core-halo morphology of FDM halos.
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All authors Flavio Rosales-Infante, Alejandro Quiñonez-Guerrero, Iván Álvarez-Rios, Francisco S. Guzmán

Astrophysics of Galaxies

ALMA Chemical Evolution (ACE) Survey: Molecular gas properties of low-mass, low-metallicity galaxies at cosmic noon

Gergő Popping, Ivanna Langan, Nikki N. Geesink et al. (+13 more)

Molecular gas plays a central role in regulating star formation and galaxy evolution, yet observational constraints at cosmic noon remain biased toward massive, metal-rich systems. We present ALMA Band 3 observations of the CO J=3-2 transition in 26 unlensed star-forming galaxies from the ALMA Chemical Evolution (ACE) Large Program at z~2-2.5, probing stellar masses of $10^{9} < M_\star < 10^{10.5}\,\mathrm{M}_{\odot}$ and sub-solar metallicities (8.2 < 12 + log(O/H) < 8.6). We derived molecular gas masses using a metallicity-dependent CO-to-H$_2$ conversion factor and alongside analysed stacking measurements and a homogenized literature compilation spanning both local and high-redshift galaxies. We find that the ACE galaxies extend established molecular-gas scaling relations to an order of magnitude lower stellar masses than previously explored at cosmic noon. The molecular gas mass ($M_{\rm mol}$) correlates tightly with star formation rate (SFR), while molecular gas fractions show a strong dependence on specific star formation rate (sSFR) and offset from the star-forming main sequence. In contrast, molecular gas fractions show only weak trends with stellar mass and no significant dependence on metallicity. Molecular gas depletion times are ~1 Gyr and vary little with stellar mass or metallicity, and weakly with sSFR and offset from the star-forming main sequence. Together this further reinforces that the availability of molecular gas is the primary driver of the SFR in galaxies, with changes in star-formation efficiency playing a secondary role. Leveraging the expanded parameter space probed by the ACE and literature samples, we derive a new empirical prescription for predicting $M_{\rm mol}$ as a function of SFR and sSFR. The persistence of the observed scaling relations suggests a largely universal framework governing the molecular gas-star formation cycle across cosmic time.
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All authors Gergő Popping, Ivanna Langan, Nikki N. Geesink, Melanie Kaasinen, Irene Shivaei, Leindert A. Boogaard, Daizhong Liu, Max Parente, Alexandra Pope, Roxana Popescu, Manuel Solimano, Bahram Mobasher, Bianca Moreschini, Desika Narayanan, Naveen Reddy, Ryan L. Sanders

Astrophysics of Galaxies

ALMA Chemical Evolution (ACE) survey: the dust content of subsolar metallicity galaxies at cosmic noon

M. Solimano, I. Shivaei, G. Popping et al. (+11 more)

Dust plays a key role in galaxy evolution by influencing star formation and shaping the observed spectrum of galaxies. However, at z~2 (cosmic noon) our knowledge of the dust mass budget is currently limited to the most massive, metal-rich systems, which are not representative of the bulk galaxy population. Here, we probe the lower mass, subsolar metallicity regime by measuring the dust mass of 25 galaxies at z~2.3 from the ALMA Chemical Evolution (ACE) Large Program. The sample contains star-forming galaxies in the COSMOS field with robust strong-line metallicities down to ~0.3 $Z_\odot$. Using the dust continuum emission detected at 873micron or 1.3mm we constrain the dust mass by assuming an optically thin single-temperature modified blackbody. The resulting dust masses average $10^{8}\,\mathrm{M}_\odot$, and they are three to nine times larger than those of z=0 galaxies at a matched metallicity and stellar mass. We also find positive correlations between dust mass and stellar mass, metallicity, and star formation rate (SFR). In contrast, we find that the $M_\mathrm{dust}/M_\mathrm{stars}$ (DtS) ratio scatters around $10^{-2.2}$ but shows no evidence of correlation with metallicity. This result is consistent with dust evolution models that predict a constant DtS once the ISM reaches the critical metallicity, at which metal accretion onto grains becomes the main mode of dust buildup. The correlation between $M_\mathrm{dust}/\mathrm{SFR}$ and metallicity also suggest that ACE galaxies have already surpassed the critical metallicity. Finally, we find that the DtS ratio is correlated to the specific SFR (sSFR). Since the sSFR are high ($> 10^{-8}\,\mathrm{yr}^{-1}$) this explains the DtS excess over z~0 galaxies. In turn, both sSFR and DtS are likely driven by the molecular gas fraction, as supported by CO(3-2) measurements taken as part of ACE.
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All authors M. Solimano, I. Shivaei, G. Popping, L. A. Boogaard, I. Langan, R. Popescu, N. N. Geesink, A. Pope, L. Arriscado, B. Mobasher, D. Narayanan, M. Parente, N. Reddy, R. Sanders

Astrophysics of Galaxies · Cross-listed from astro-ph.EP

The Galactic Dynamics of Free-Floating Planets: From Ejection Kicks to Microlensing

Zara Sayed, Stefano Profumo and Nolan Smyth

Free-floating planets (FFPs) may retain dynamical signatures of the mechanisms that eject them from their host systems. We integrate $10^6$ collisionless FFP test particles for $10^8$~yr in a static, phenomenological Galactic potential, comparing a mass-independent kick model with a mass-coupled prescription ($\sigma_{\rm CB}\propto M^{-0.15}$, $v_{\rm PL}\propto M^{-0.5}$) against a matched no-kick control. The imposed mass dependence is recovered at injection, with the combined-channel median coupled kick decreasing from $10.716$ to $0.708~{\rm km\,s^{-1}}$ across five mass bins—a factor of $\sim15.1$. A mass-dependent trend remains visible after $100$~Myr of Galactic propagation in the matched kicked-versus-control displacement, whose median decreases from $0.7001$ to $0.0539$~kpc across the same bins. The remaining numerical distinction is concentrated in this mass-resolved differential displacement rather than in the bulk phase-space moments: the final velocity dispersions of the null and coupled kicked populations are nearly identical, only a few percent of particles leave the adopted disk region, and the fraction of particles satisfying the formal Galactic-unbound criterion ($E_i>0$) remains negligible in every diagnostic we report. Comparing each kicked population against its matched no-kick control shows that much of the overall kinematic heating arises from the evolution of the initially warm, nonequilibrium disk rather than from the ejection kick itself, isolating the kick's smaller contribution.
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Astrophysics of Galaxies

What Drives Galaxy-Galaxy Differences In The Selective Attenuation Curve? New Perspectives from DESI DR1

Andrew Mizener, Daniela Calzetti, Ranga-Ram Chary et al. (+1 more)

Leveraging a sample of 3457 galaxies drawn from DESI DR1 and cross-matched with archival GALEX UV photometry, we construct new dust attenuation curves and measure how the shape of these curves vary as a function of galaxy properties. Our curves are built by comparing the median flux densities of galaxies that have been divided into bins of nebular opacity, measured via the Balmer optical depth (i.e. the H$\alpha$/H$\beta$ ratio). When no further cuts on galaxy properties are applied, we find an attenuation curve very similar to previous work at low redshifts. We then test how the attenuation curves vary as a function of galaxy properties; stellar mass, specific star formation rate, metallicity, and ionization parameter. We find that the curve steepens significantly at higher specific star formation rate. In our data, there is not a clear link between the ionization parameter, mass, or metallicity and the attenuation curve slope.
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All authors Andrew Mizener, Daniela Calzetti, Ranga-Ram Chary, John Moustakas

Astrophysics of Galaxies

Sown at Cosmic Dawn: Searching for Pop III Signatures in JWST JADES He II Selected Line Emitters

Rosa Roberts, Giorgia Riley, Christopher J. Conselice et al. (+4 more)

Population III (Pop III) stars, the first generation of metal-free stars, remain undetected, partly because entirely pristine galaxies represent a short-lived phase. We instead target the longer-lived self-polluted and hybrid Pop III-Pop II phases, in which surviving metal-free Pop III stars coexist with enriched gas and newly formed Pop II stars, producing strong He II alongside detectable UV metal lines. We search for this signature in 84 strong He II-emitting galaxies at z = 3-7 in the JWST/JADES GOODS-South and GOODS-North fields, combining UV emission-line diagnostics, gas-phase metallicities, AGN screening, and spatially resolved SED fitting. We find no evidence for any pristine Pop III galaxies. Instead, The Blueberry (ID 13176, z = 5.94) is our strongest candidate for a hybrid Pop III-Pop II system and is the only source with robust detections of all diagnostic UV lines. Its resolved stellar populations are extremely young, blue, and weakly attenuated, with high star formation rates, consistent with intense recent star formation. While these properties alone cannot distinguish it from a chemically enriched starburst, its robust UV metal-line ratios provide the strongest evidence in our sample for a surviving Pop III contribution within an enriched host. The Carrot (ID 13577, z = 5.57) further demonstrates the power of resolved analysis, revealing a central region substantially bluer and younger than the galaxy as a whole. Together, these results suggest that Pop III signatures may be spatially localised and diluted in integrated measurements, highlighting resolved SED fitting as a tool for identifying environments where the Universe's first stars may survive.
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All authors Rosa Roberts, Giorgia Riley, Christopher J. Conselice, Duncan Austin, Thomas Harvey, Lewi Westcott, Jordan C. J. D'Silva

Astrophysics of Galaxies

Euclid Quick Data Release (Q1) Euclid spectroscopy of quasars. 2. Physical properties from spectral fitting

Euclid Collaboration: J. Calhau, G. Calderone, A. Feltre et al. (+311 more)

A substantial volume of spectroscopic data has become available with the Euclid Data Release (Q1), which represents a unique opportunity to study quasars (QSOs) in the Euclid Deep Fields, provide spectroscopic measurements, and estimates of their physical properties. We present results from a spectroscopic analysis of QSOs with HE < = 22.5 using Q1. We use external catalogues from surveys such as the Dark Energy Spectroscopic Instrument (DESI), Gaia, Wide-field Infrared Survey Explorer (WISE), and the QUasars as BRIght beacons for Cosmology in the Southern hemisphere (QUBRICS) for the QSO selection and redshift determination, totaling 5489 QSOs. We provide measurements of the line fluxes, full widths at half-maximum, and respective uncertainties for the emission lines of Euclid spectra based on fitting statistica and signal-to-noise ratio (S/N). Of the total 5489 QSOs, 5387 are successfully fitted. We find that 45% of the total number of successfully fitted spectra are free of problematic artefacts allowing for trustworthy measurements. Our final Euclid QSO sample spans a redshift range of 0.01 < = z < = 4.8 and shows a median spectral index of {\alpha}{\lambda} = - 1.17. Finally, we estimate black hole masses with single epoch methods for 1213 sources, using the He I {\lambda}10830, Pa {\beta}, H {\alpha}, H {\beta}, and Mg II emission lines, obtainning a mean logarithmc mass of log10 (MBH / Msolar) = 8.7 and mean Edigton ratio of {\lambda}Edd = 0.34. The catalogue with the physical properties of this sample together with the software developed for the analysis is available online for scientific exploitation.
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All authors Euclid Collaboration: J. Calhau, G. Calderone, A. Feltre, M. Scialpi, V. Allevato, H. Landt, F. Ricci, Y. Fu, L. Spinoglio, F. Shankar, L. Nicastro, A. Viitanen, G. Zamorani, M. Mezcua, F. La Franca, D. Stern, E. Lusso, J. Wolf, A. Paulino-Afonso, S. Andreon, N. Auricchio, C. Baccigalupi, M. Baldi, S. Bardelli, P. Battaglia, A. Biviano, M. Bolzonella, E. Branchini, M. Brescia, S. Camera, V. Capobianco, C. Carbone, J. Carretero, M. Castellano, G. Castignani, S. Cavuoti, K. C. Chambers, A. Cimatti, C. Colodro-Conde, G. Congedo, C. J. Conselice, L. Conversi, Y. Copin, F. Courbin, H. M. Courtois, M. Cropper, H. Degaudenzi, G. De Lucia, H. Dole, F. Dubath, X. Dupac, S. Dusini, A. Ealet, S. Escoffier, M. Farina, S. Ferriol, F. Finelli, S. Fotopoulou, N. Fourmanoit, M. Frailis, M. Fumana, L. Gabarra, S. Galeotta, K. George, B. Gillis, C. Giocoli, J. Gracia-Carpio, A. Grazian, F. Grupp, W. G. Hartley, S. V. H. Haugan, S. Hemmati, W. Holmes, I. M. Hook, F. Hormuth, A. Hornstrup, M. Huertas-Company, K. Jahnke, M. Jhabvala, B. Joachimi, S. Kermiche, A. Kiessling, B. Kubik, M. Kümmel, M. Kunz, H. Kurki-Suonio, A. M. C. Le Brun, V. Le Brun, S. Ligori, P. B. Lilje, V. Lindholm, I. Lloro, M. Magliocchetti, G. Mainetti, O. Mansutti, O. Marggraf, M. Martinelli, N. Martinet, F. Marulli, R. J. Massey, N. Mauri, E. Medinaceli, S. Mei, M. Meneghetti, E. Merlin, G. Meylan, P. Monaco, A. Mora, M. Moresco, C. Moretti, L. Moscardini, C. Neissner, S.-M. Niemi, J. W. Nightingale, C. Padilla, S. Paltani, F. Pasian, K. Pedersen, W. J. Percival, V. Pettorino, A. Pezzotta, S. Pires, G. Polenta, M. Poncet, L. A. Popa, L. Pozzetti, F. Raison, R. Rebolo, A. Renzi, J. Rhodes, G. Riccio, I. Risso, E. Romelli, M. Roncarelli, B. Rusholme, R. Saglia, Z. Sakr, D. Sapone, B. Sartoris, P. Schneider, T. Schrabback, M. Scodeggio, A. Secroun, E. Sihvola, P. Simon, C. Sirignano, G. Sirri, L. Stanco, C. Surace, P. Tallada-Crespí, A. N. Taylor, H. I. Teplitz, I. Tereno, S. Toft, R. Toledo-Moreo, F. Torradeflot, I. Tutusaus, J. Valiviita, T. Vassallo, D. Vibert, Y. Wang, J. Weller, A. Zacchei, E. Zucca, M. Ballardini, P. Bergamini, S. Borgani, E. Bozzo, C. Burigana, R. Cabanac, A. Cappi, T. Castro, J. A. Escartin Vigo, J. García-Bellido, T. Gasparetto, A. Loureiro, J. Macias-Perez, R. Maoli, R. B. Metcalf, M. Pöntinen, E. Sarpa, V. Scottez, M. Sereno, M. Tenti, M. Tucci, M. Viel, M. Wiesmann, J. A. Acevedo Barroso, Y. Akrami, I. T. Andika, G. Angora, S. Anselmi, M. Archidiacono, G. Arico, F. Atrio-Barandela, E. Aubourg, M. Baes, L. Baumont, L. Bazzanini, D. Bertacca, M. Bethermin, F. Beutler, L. Bisigello, A. Blanchard, L. Blot, M. L. Brown, S. Bruton, A. Calabro, B. Camacho Quevedo, F. Caro, C. S. Carvalho, F. Cogato, T. E. Collett, S. Conseil, A. R. Cooray, P. Corcho-Caballero, B. Csizi, O. Cucciati, H. Dannerbauer, S. Davini, T. de Boer, F. De Paolis, G. Desprez, A. Díaz-Sánchez, S. Di Domizio, J. M. Diego, V. Duret, A. Enia, Y. Fang, A. Farina, A. G. Ferrari, A. Finoguenov, F. Fontanot, A. Franco, K. Ganga, R. Gavazzi, E. Gaztanaga, Z. Ghaffari, F. Giacomini, F. Gianotti, G. Gozaliasl, A. Gruppuso, M. Guidi, C. M. Gutierrez, A. Hall, N. A. Hatch, H. Hildebrandt, J. Hjorth, J. J. E. Kajava, Y. Kang, V. Kansal, D. Karagiannis, J. Kim, C. C. Kirkpatrick, A. Kovács, I. Kovačić, K. Koyama, S. Kruk, M. C. Lam, G. Leroy, J. Lesgourgues, L. Linke, S. J. Liu, X. Lopez Lopez, G. Maggio, F. Mannucci, F. R. Marleau, C. J. A. P. Martins, M. Migliaccio, M. Miluzio, G. Morgante, S. Nadathur, K. Naidoo, A. Navarro-Alsina, A. Nersesian, S. Nesseris, F. Oppizzi, F. Pace, D. Paoletti, F. Passalacqua, K. Paterson, L. Patrizii, A. Pisani, D. Potter, G. W. Pratt, S. Quai, M. Radovich, G. Rodighiero, K. Rojas, W. Roster, S. Sacquegna, M. Sahlén, D. B. Sanders, A. Schneider, D. Sciotti, E. Sellentin, S. Serjeant, J. G. Sorce, M. Talia, K. Tanidis, C. Tao, F. Tarsitano, G. Testera, R. Teyssier, S. Tosi, A. Troja, C. Uhlemann, C. Valieri, A. Venhola, G. Verza, S. Vinciguerra, M. von Wietersheim-Kramsta, L. Wang, A. H. Wright

Astrophysics of Galaxies · Cross-listed from astro-ph.SR

White Dwarf Natal Kicks as Velocity-Space Random Walks. II. Binary Stellar Evolution and Observational Kick Constraints

Dang Pham, Stephen Majeski, Taeho Ryu et al. (+2 more)

Wide binaries containing white dwarfs (WDs) provide a pathway to exploring post-main-sequence (MS) natal kicks associated with asymmetric mass loss. In this work, we develop a binary population synthesis model that involves episodic mass loss and velocity kicks during the thermally-pulsing asymptotic-giant-branch (TP-AGB) phase of stellar evolution, when mass loss is expected to be most significant. We compare our synthesized populations against the Gaia DR2 and DR3 data for wide WD-MS and WD-WD binaries, varying the number, strength, and directionality of TP-AGB kicks. We find that the observed separation distribution can constrain the kick strength, but it alone is insufficient to also constrain the kick number and dimensionality. We therefore additionally constrain our models using the observed eccentricity distributions. Models where mass loss induces a random walk in the star's velocity are most consistent with observed eccentricity constraints for WD-MS binaries. No models are found to agree with the WD-WD eccentricity constraint. Our results suggest that at least 10 randomly directed kicks take place during the TP-AGB phase, leading to a cumulative root-mean-square kick velocity of approximately 0.7 km/s. These findings constrain the nature of WD natal kicks, connecting the orbital distributions of evolved wide binaries to asymmetric mass loss during the final stages of stellar evolution.
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All authors Dang Pham, Stephen Majeski, Taeho Ryu, Gabriel Tomassini, Andrea Chiavassa

Astrophysics of Galaxies · Cross-listed from astro-ph.SR

White Dwarf Natal Kicks as Velocity-Space Random Walks. I. Fokker-Planck Theory

Stephen Majeski, Dang Pham, Taeho Ryu et al. (+2 more)

White dwarfs are the most common end state of stellar evolution, including that of our own Sun, making their formation critical to completing a more comprehensive understanding of stellar evolution and even determining the eventual fate of the solar system. Wide binaries containing white dwarfs offer a powerful probe: their components evolve largely independently, yet stellar mass loss and velocity impulses (natal kicks) on the white dwarf progenitor leave measurable imprints on orbital properties. Previous population studies typically assume that each white dwarf receives only a single natal kick as it forms. While convenient, this simplification conflicts with simulations finding the formation process to be episodic. Therefore, a more realistic picture is that white-dwarf progenitors experience multiple stochastic kicks over their evolution. Here, we present a Fokker-Planck model for the evolution of binary orbital parameter distributions subject to many, randomly-oriented mass-loss-driven kicks. This model recovers key features of white-dwarf binary observations, including a -2 power law tail in the probability distribution of separations, and the thermalization of binary eccentricities beyond separations of 1000 au. We additionally investigate how white-dwarf kicks impact a myriad of other processes, such as binary dissolution, planetary system evolution, and even the production of interstellar objects.
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All authors Stephen Majeski, Dang Pham, Taeho Ryu, Gabriel Tomassini, Andrea Chiavassa

Astrophysics of Galaxies

Cosmic web Ly$\alpha$ emission in a sample of overdense regions

Davide Tornotti, Michele Fumagalli, Matteo Fossati et al. (+7 more)

We present a complete and homogeneous analysis of the Ly$\alpha$ emission properties of the cosmic web at $3 \lesssim z \lesssim 5$ as a function of the overdensity of Ly$\alpha$ emitters (LAEs) in the MUSE Ultra Deep Field (MUDF) and the MUSE Extremely Deep Field (MXDF). We identify 41 overdensities, probing environments that are $\delta \approx 2 - 10$ times denser than the field. We search for extended emission down to surface brightness (SB) levels of $3 - 5 \times 10^{-20}\ \mathrm{erg\ s^{-1}\ cm^{-2}\ arcsec^{-2}}$, revealing filamentary structures beyond the scale of the circumgalactic medium, confirming that LAEs act as signposts of the cosmic web. A trend with overdensity emerges: non-detections are mainly at $\delta < 2$, a $\approx 1$ dex scatter in SB appears for $2 \lesssim \delta \lesssim 3.5$, and detections reach a maximum intrinsic SB of $\approx 2 \times 10^{-19}\ \mathrm{erg\ s^{-1}\ cm^{-2}\ arcsec^{-2}}$ for $\delta \gtrsim 3.5$. Emitting regions occupy a fraction of projected area $f_s \approx 0.20 - 0.25$ inside filaments, yielding a cosmological incidence for Ly$\alpha$ emission in the cosmic web $\ell(\mathrm{Ly}\alpha)$ of $\approx 1.22$, which is similar to the one of partially-neutral Lyman limit systems. This analysis indicates that the emitting gas is partially ionized at moderate densities ($n_{\mathrm{H}} \approx 10^{-3} - 10^{-1}\ \mathrm{cm}^{-3}$), likely tracing the denser spines of intergalactic filaments and embedded substructures. Finally, we forecast how oriented stacking in larger samples of overdensities from shallower observations could yield an expanded view of the cosmic web before the next-generation wide-field spectroscopic instruments become operational.
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All authors Davide Tornotti, Michele Fumagalli, Matteo Fossati, Roland Bacon, Fabrizio Arrigoni Battaia, Rajeshwari Dutta, Michele Fulghieri, Celine Peroux, Marc Rafelski, Mitchell Revalski

Astrophysics of Galaxies

An Archival Calibration of JWST/MIRI Prism Wide-Field Slitless Spectroscopy: Methodology, Performance, and a Mid-Infrared Spectral Atlas of Galaxies at $z=0-4$ in the GOODS-N/S Fields

Fengwu Sun, Javier Álvarez-Márquez, Eiichi Egami et al. (+4 more)

Through the Low Resolution Spectroscopy (LRS) observing mode of JWST/MIRI, the P750L prism disperses the entire ~70"$\times$110" imager field, turning MIRI into a wide-field slitless spectrograph (WFSS) at 5-14 $\mu$m with spectral resolution $R\sim100$. Using archival MIRI LRS data taken in the GOODS-N/S deep fields and calibration programs, we present a complete and precise calibration suite for MIRI WFSS through an AI-assisted agentic workflow under human supervision. The calibration includes flat field, sky background, spectral tracing, wavelength calibration, flux calibration, and the large-scale flux flat (L-flat). We present the methodology of each calibration and quantify its accuracy. As a demonstration, we extract 5-14 $\mu$m slitless spectra of 180 spectroscopically confirmed galaxies at $z=0.08 - 3.71$ in the GOODS-N/S fields. We detect a large number of polycyclic aromatic hydrocarbon (PAH) bands and atomic lines (including Paschen $\alpha$ out to $z=3.71$) in individual sources. The PAH 3.3 $\mu$m luminosities correlate with the Paschen $\alpha$ luminosities (measured through NIRCam WFSS) for $z\sim1$ galaxies over a $\sim$1.5-dex range, supporting PAH 3.3 $\mu$m as a star-formation-rate tracer out to $z\sim1.6$. We release the calibration reference files, reduction scripts, and the mid-infrared spectral atlas. We also present caveats and lessons learned from our archival calibration work. Our empirical sensitivity characterization identifies a noise floor for deep MIRI WFSS integrations ($\gtrsim$ a few ks), whereas shallower integrations exceed the sensitivity predicted by the JWST Exposure Time Calculator. We also provide suggestions for the planning of future MIRI WFSS observing programs.
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All authors Fengwu Sun, Javier Álvarez-Márquez, Eiichi Egami, Román Fernández Aranda, Jakob M. Helton, Xiaojing Lin, Jianwei Lyu

Astrophysics of Galaxies

Quiescent Galaxies at $z > 2$ from CAPERS spectroscopy and their Number densities

Lu Shen, Weida Hu, Casey Papovich et al. (+28 more)

Recent JWST observations have revealed an overabundance of quiescent galaxies at high redshift. Photometric methods, such as photometry-derived sSFRs, $UVJ$ colors, and synthetic $ugi_s$ colors, are commonly used to identify quiescent galaxies, but their completeness and purity remain poorly constrained. Here we present a spectroscopically selected sample of 19 quiescent galaxies at $2 \leq z \leq 4$ from the CANDELS-Area Prism Epoch of Reionization Survey (CAPERS). They are selected with $M_\ast > 10^{9.5} M_\odot$ and a specific star formation rate below 20% of the inverse cosmic age. These galaxies formed 50% of their stellar mass at $z \sim 3.0$–4.6 and quenched rapidly on timescales of $\sim0.1$–0.2 Gyr. These quenching timescales are comparable to those of other high-redshift QGs but shorter than those at lower redshift. Using the spectroscopic sample as a benchmark, we assess commonly adopted photometric QG selection methods. We find completeness of 63–89% and purities of only 40–63%, with strong emission-line galaxies constituting the dominant source of contamination. Applying completeness and purity corrections calibrated from the spectroscopic sample, we measure the number density of quiescent galaxies at $2 \leq z \leq 5$. The resulting number densities exceed the predictions of most current galaxy-formation simulations at $2<z<4$, with the largest discrepancy at $M_\ast \geq 10^{10.5} M_\odot$. This discrepancy suggests that current cosmological models may not assemble and quench massive galaxies sufficiently early or efficiently.
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All authors Lu Shen, Weida Hu, Casey Papovich, Justin Cole, Mark Dickinson, Pablo Arrabal Haro, Anthony J. Taylor, Adam C. Carnall, Ángel Chandro-Gómez, Yingjie Cheng, Nikko J. Cleri, James S. Dunlop, Carter Flayhart, Steven L. Finkelstein, Mauro Giavalisco, Michaela Hirschmann, Eric F. Jiménez-Andrade, Jeyhan S. Kartaltepe, Claudia D.P. Lagos, Ho-Hin Leung, Arianna S. Long, Ray A. Lucas, Eric J. Murphy, Lorenzo Napolitano, Pablo G. Pérez-González, Raymond C. Simons, Struan D Stevenson, Elizabeth Taylor, Xin Wang, L. Y. Aaron Yung, Jorge A. Zavala

Astrophysics of Galaxies

The Galactic Phosphorus Survey. I. Chemical Evolution across the Galactic Disk from $\sim$750 FGK Stars

Dionysios Gakis, Keith Hawkins, Zachary G. Maas et al. (+5 more)

Phosphorus (P) is an odd-$Z$ element produced primarily in massive stars and is also important for planetary chemistry as an element essential to life. However, its evolution over cosmic time remains poorly constrained because precise and homogeneous stellar P measurements are scarce. We determine the relationship between [P/Fe] and [Fe/H] over a range of metallicities across the Galactic disk and assess its variation between different stellar populations using the largest uniformly analyzed sample to date, comprising $\sim$750 FGK stars with high-resolution near-infrared spectra. Stellar parameters are determined through a spectro-photometric approach and P abundances are derived by fitting synthetic spectra to the P~I 10529.52~Å\ absorption feature. We confirm that [P/Fe] increases toward lower metallicities down to [Fe/H] $\sim$ -1.0 dex, where it appears to peak, broadly resembling the rise seen in $\alpha$-element abundance ratios over the same metallicity range and supporting a dominant contribution from massive stars on short core-collapse supernova timescales. When separating the sample into Galactic disk populations, thick-disk stars are systematically enhanced in [P/Fe] relative to the thin disk by $\sim$0.08 dex at fixed metallicity. We also measure a radial [P/Fe] gradient of $-0.124 \pm 0.006$ dex kpc$^{-1}$ and a vertical gradient of $+0.052 \pm 0.007$ dex kpc$^{-1}$. Although current chemical evolution models struggle to reproduce the observed trends, this survey increases the number of homogeneously measured stellar P abundances by approximately a factor of three, providing a new benchmark for Galactic chemical evolution models and the phosphorus inventory available to planetary systems.
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All authors Dionysios Gakis, Keith Hawkins, Zachary G. Maas, Christopher Sneden, Melike Afşar, Natalie R. Hinkel, Chenguang Sun, Wenwei Liang

Astrophysics of Galaxies

From IFS Maps to 3D Structure I: Constraining Geometry in the Circumgalactic Medium

Mandy C. Chen, Michael Rauch, Zhijie Qu et al. (+3 more)

The three-dimensional geometric structure of the cool (T~$10^4$ K) circumgalactic medium (CGM) – the line-of-sight depth and the number of discrete clumps – is poorly constrained. Existing inferences come predominantly from quasar absorption-line statistics, but these pencil-beam probes provide limited spatial and kinematic information. Here we show that spatially resolved emission-line maps from integral field spectrograph (IFS) observations provide complementary, novel constraints on cool CGM geometry when projection effects are accounted for. Observations of a sample of CGM nebulae yield measurements of the line-of-sight and the plane-of-sky velocity dispersions, with ratios $\sigma_{\rm los}/\sigma_{\rm pos}$ ranging from ~1 to ~2.5. Using direct numerical simulations of isotropic turbulence projected through emitting slabs of varying depth $L_{\rm los}$, we show that the ratio $\sigma_{\rm los}/\sigma_{\rm pos}$ allows us to probe $L_{\rm los}/L_{\rm neb}$, where $L_{\rm neb}$ is the nebular extent on the plane of the sky. We find that the inferred line-of-sight depth is typically ~0.1-$5\,L_{\rm neb}$, indicating that these nebulae are broadly comparable in depth and projected extent. Although the cool CGM is intrinsically clumpy, at the current IFS data resolution, each beam aggregates enough clumps that the projected dispersion ratio approaches its volume-filling value. Consequently, the emission kinematics provide little additional information on the detailed clump configuration beyond consistency with the clump incidence rates inferred from absorption-line surveys. These findings serve as a theoretical framework for the turbulence diagnostics developed in the companion paper (Paper II). Together, these papers demonstrate how IFS emission-line kinematics can provide a quantitative probe of the 3D CGM, complementary to absorption-line and emerging FRB approaches.
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All authors Mandy C. Chen, Michael Rauch, Zhijie Qu, Gwen C. Rudie, Hsiao-Wen Chen, James R. Beattie

Astrophysics of Galaxies · Cross-listed from astro-ph.SR

The Treasury of Extremely Metal-Poor O Stars

O. Grace Telford, Christiana Erba, Kristen B. W. McQuinn et al. (+10 more)

The Treasury of Extremely Metal-Poor O Stars (TEMPOS) is a Hubble Space Telescope survey of hot and massive O-type stars in nearby, low-metallicity galaxies ($\lesssim$20% of the solar metallicity, $Z_\odot$). Understanding massive-star physics in this regime is essential to interpret observations of metal-poor galaxies, including both low-mass dwarf galaxies and chemically unevolved galaxies in the early Universe. Yet, few far-ultraviolet (FUV) spectra of O stars of sufficient quality to characterize their fundamental properties and stellar winds exist below 20% $Z_\odot$, and heterogeneous observation design and incomplete coverage of parameter space pose significant barriers to progress. To remedy this, TEMPOS obtained new Cosmic Origins Spectrograph (COS) FUV spectra of 12 very metal-poor O stars, building upon archival data to assemble a spectroscopic atlas of 29 homogeneously observed stars that efficiently samples a wide range of spectral types and luminosity classes. Here, we describe the motivation, sample selection, and observation design for TEMPOS and present the first data release of reduced and coadded COS spectra. We then present initial results on the empirical properties of FUV O-star spectra below 20% $Z_\odot$, including radial velocities, equivalent widths of photospheric lines, and terminal wind velocities ($v_\infty$). We show that $v_\infty$ correlates with host galaxy metallicity across $\sim$5-50% $Z_\odot$ and find tentative evidence of a steeper decline in wind strength below $\sim$10% $Z_\odot$. The combined dataset of FUV spectra and planned releases of photometry and optical spectra from the TEMPOS Treasury program will advance our understanding of both stellar astrophysics and the interstellar medium in the extremely metal-poor regime.
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All authors O. Grace Telford, Christiana Erba, Kristen B. W. McQuinn, Calum Hawcroft, Andreas A. C. Sander, Julia Roman-Duval, John Chisholm, Danielle A. Berg, Varsha Ramachandran, Yong Zheng, Claus Leitherer, Abby Mintz, Evan N. Kirby

Astrophysics of Galaxies

ALMA Chemical Evolution (ACE) survey: dust-to-gas ratios in sub-solar metallicity galaxies at cosmic noon

N. N. Geesink, G. Popping, L. A. Boogaard et al. (+11 more)

Dust is a fundamental component of the interstellar medium and provides a key tracer of the baryon cycle that regulates galaxy evolution. The dust-to-gas ratio links metals in the gas phase to those locked into dust grains, making it a sensitive diagnostic of dust production, grain growth, and destruction. We present measurements of the dust-to-molecular-gas ratio ($\rm DGR_{mol}$), for typical star-forming galaxies ($\log M_\star \approx 10$) at sub-solar metallicites, at $z\simeq2-2.5$ from the ALMA Chemical Evolution (ACE) survey. By combining ALMA CO and dust-continuum observations with robust gas-phase metallicity measurements, ACE extends direct dust and molecular-gas measurements to lower stellar masses and lower metallicities than previously available at this epoch, reaching down to $0.4\,Z_{\odot}$. This enables the first constraints on the $\rm DGR_{mol}$–metallicity relation for typical unlensed galaxies at cosmic noon. We find that $\rm DGR_{mol}$ increases with metallicity, with a log-space slope of $1.2 \pm 0.7$, indicating that metal-poor galaxies have systematically lower $\rm DGR_{mol}$ than their more metal-rich counterparts. For the detected ACE galaxies, we measure a mean value of $\log_{10}(M_{\rm dust}/M_{\rm mol})=-2.37\pm0.05$ for a mean metallicity of 12+$\log (\rm O/H) = 8.45 \pm 0.02$. We find agreement with $\rm DGR_{mol}$ in the local Universe at fixed metallicities, indicating that the same dust-growth physics, likely grain growth in the ISM, dominates at metallicities of $8.3 \leq 12+\log(\rm O/H) \leq 8.7$ at cosmic noon. These measurements provide novel empirical constraints for models of dust enrichment and galaxy evolution during the peak epoch of cosmic star formation. Additionally, ACE provides a sub-solar metallicity reference for the calibration of dust continuum as tracer of molecular gas, essential for studying metal-poor, high-redshift systems.
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All authors N. N. Geesink, G. Popping, L. A. Boogaard, I. Langan, A. Pope, R. Popescu, I. Shivaei, M. Solimano, M. Kaasinen, B. Mobasher, D. Narayanan, M. Parente, N. Reddy, R. L. Sanders

Astrophysics of Galaxies

ALMA Chemical Evolution (ACE) survey: The gas fundamental metallicity relation at cosmic noon

I. Langan, I. Shivaei, G. Popping et al. (+11 more)

Chemical enrichment shapes how galaxies form and evolve. The gas-phase metallicity is directly linked to the stellar mass, star formation rate, and cold gas of the interstellar medium. Thus, the cold gas fundamental metallicity relation (GFMR) is a powerful tool for probing galaxy evolution, bridging large-scale gas flows modulating the cold gas reservoir and small-scale metal enrichment tracing the cumulative impact of star formation. Constraining all these properties for the same representative sample of galaxies remains challenging yet essential. Using CO(3–2) band 3 observations from the Atacama Large Millimeter/submillimeter Array Chemical Evolution (ACE) survey, we investigated the GFMR in a sample of 26 main-sequence (log(M_*, med)=9.96), subsolar-metallicity (12+log(O/H)_med=8.44) star-forming galaxies (SFGs) at z~2. With 17/26 CO detections, including some of the lowest-metallicity CO detections at cosmic noon, we find that the stellar mass remains the primary driver of the chemical evolution in our sample (sigmaMZR~0.10). Whereas the molecular gas likely plays a secondary role (sigmaGFMR~0.11) similar to that of the star formation rate (sigmaFMR~0.13). This likely reflects our sensitivity to only the CO-bright component of the molecular reservoir. Our results remain consistent with gas-regulator models and suggest the existence of efficient molecular outflows, with an average mass loading factor of eta~4, regulating star formation and chemical enrichment.
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All authors I. Langan, I. Shivaei, G. Popping, L. A. Boogaard, N. N. Geesink, M. Kaasinen, A. Pope, R. Popescu, M. Solimano, L. Arriscado, D. Narayanan, M. Parente, N. Reddy, R. L. Sanders

Astrophysics of Galaxies

Free-Free Radio Emission from Little Red Dots as a Probe of Ionized Gas

Takumi S. Tanaka, Kohei Inayoshi, Zu Yan et al. (+3 more)

Recent studies have hypothesized that little red dots (LRDs) are rapidly accreting black holes surrounded by dense gaseous environments. Both neutral and ionized gas play a key role in explaining many of the puzzling spectral features of LRDs, including the emission line profiles in the optical-infrared bands, although the physical conditions required for these gas components remain poorly constrained. We propose that free-free emission provides a robust, independent probe of ionized gas in LRDs. Free-free self-absorption produces a characteristic spectral turnover whose critical frequency and luminosity depend on the electron column density and the characteristic size of the ionized region, such that radio observations simultaneously constrain both quantities. The spectral slope at frequencies below the turnover further probes the radial density distribution on spatial scales far below those achievable by current and future optical-infrared observatories. We also present predicted free-free spectral energy distributions for two representative LRDs in the local and high-redshift universe and show that future radio-to-millimeter observations with ALMA and ngVLA can probe the range of ionized-gas parameters inferred from current observations. Free-free emission therefore offers a unique way to probe the geometry and physical conditions of the ionized gas surrounding LRDs.
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All authors Takumi S. Tanaka, Kohei Inayoshi, Zu Yan, Tomokazu Kiyota, Yuichi Harikane, John D. Silverman

Astrophysics of Galaxies

A near-IR survey of luminous asymptotic giant branch stars in the satellites and stellar halo of M31

Jess M. Howell, Annette M. N. Ferguson, Olivia C. Jones et al. (+5 more)

We investigate the dwarf spheroidal (dSph) satellites and stellar halo of M31 using near-infrared imaging from the Wide-Field Camera on the UKIRT 3.8 m telescope. Our homogeneous analysis covers the stellar extents of 12 dSphs, as well as their surrounding halo field populations. We identify carbon-rich (C) and oxygen-rich (M) thermally-pulsing AGB stars (TP-AGBs) using colour-magnitude and colour-colour diagrams, which also allows for effective contaminant rejection. TP-AGB stars are detected in eight of the 12 dSphs, indicating small intermediate-age populations in a substantial fraction of the sample; they are also found in considerable numbers throughout most of M31's stellar halo. By combining 316 new detections with a revised classification of objects previously reported in the literature, we increase the TP-AGB candidate population in the dSphs from 82 to 359. We use the resulting dSph and halo AGB samples to compute C/M ratios and infer metallicities in the dSphs and adjacent halo fields with non-zero AGB counts. A clear metallicity gradient is observed in the M31 stellar halo out to ~150 kpc, consistent with that found using other tracers. Using literature star formation histories from main-sequence turn-off photometry, we find a tight correlation between the number of C stars in the dSphs and the stellar mass formed in the last 0.5–3 Gyr. This study underscores the promise of AGB stars as quantitative tracers of intermediate-age star formation, particularly in intrinsically faint systems, and provides a catalogue of candidate TP-AGB stars for follow-up.
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All authors Jess M. Howell, Annette M. N. Ferguson, Olivia C. Jones, Mike. J. Irwin, Maria-Rosa L. Cioni, Geraint F. Lewis, Nicolas. F. Martin, Alan. W. McConnachie

Astrophysics of Galaxies

Local constraints on alcohol–thioalcohol analogs in G35.2N

Xuefang Xu, Shanghuo Li, Qian Gou et al. (+6 more)

The chemistry of sulfur-bearing complex organic molecules in dense star-forming environments remains uncertain, partly because the dominant sulfur reservoirs in dense gas and ices are poorly identified. Alcohol–thioalcohol pairs allow direct comparisons of structurally related O- and S-bearing molecules. We present ALMA Band 6 observations of CH$_3$OH/CH$_3$SH and C$_2$H$_5$OH/C$_2$H$_5$SH toward three spectral-extraction positions (MM3-pos, MM4-pos, and MM5-pos) in the MM3–MM5 region of G35.2N. Local thermodynamic equilibrium modeling yields column densities and abundance ratios. CH$_3$OH column densities were inferred from $^{13}$CH$_3$OH assuming $^{12}$C/$^{13}$C = 50 to mitigate optical-depth effects. CH$_3$OH, CH$_3$SH, and C$_2$H$_5$OH are robustly constrained at all three positions; C$_2$H$_5$SH is robustly constrained at MM3-pos and MM5-pos but remains tentative at MM4-pos. The corresponding adopted column-density ranges are $(1.8-2.7)\times10^{18}$, $(1.7-2.6)\times10^{16}$, $(5.7-8.5)\times10^{16}$, and $(2.4-4.6)\times10^{15}$ cm$^{-2}$. The CH$_3$OH/C$_2$H$_5$OH and CH$_3$OH/CH$_3$SH ratios are consistent across the positions within uncertainties, with nominal values of 31–32 and 100–110, respectively. Comparisons with chemically rich sources and warm-up chemical models show that CH$_3$OH/C$_2$H$_5$OH lies within the range measured elsewhere, whereas CH$_3$OH/CH$_3$SH exhibits greater source-to-source variation. The ethyl-level O/S comparison remains less certain because many literature C$_2$H$_5$SH measurements provide only lower limits. CH$_3$OH/CH$_3$SH is thus the best-constrained O/S alcohol–thioalcohol ratio in these data and provides an empirical probe of source-dependent sulfur-bearing organic chemistry. More sensitive C$_2$H$_5$SH observations are needed to test C$_2$H$_5$OH/C$_2$H$_5$SH.
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All authors Xuefang Xu, Shanghuo Li, Qian Gou, Chunguo Duan, Laurent Pagani, Di Li, Jun Kang, Jiaxin Du, Jiaxiang Jiao